Bagworms are caterpillars that feed on many evergreens and a variety of deciduous plants. Significant populations on evergreens can eventually lead to plant death.
On deciduous plants, it’s not as big of a concern because the leaves drop each year. However, if you have evergreens in the landscape, it’s only a matter of time before they will find their way from the deciduous plants to the evergreens.
There is a good reason to look for them on plants now, as opposed to later in the summer: When they are really small and newly hatched, they are susceptible to a pesticide called Bacillus thuringiensis var. kurstaki or Btk.
Btk is a naturally occurring biological control and extremely safe to use in the landscape. Btk does not kill the good guys such as predators or parasitoids.
The downside to Btk is that it only works on the very young, small caterpillars. Therefore, if you can spray early, you can use Btk and do a pretty good job of killing a lot of them.
After the bagworm caterpillar hatches, it produces a thin strand of silk. This silk catches in the wind and balloons in the air until the caterpillar finds a suitable host. This ballooning makes it easy for these pests to spread from plant to plant in the landscape.
Once the bagworm caterpillar settles down, it begins to feed on the foliage and construct their “bags.” The bags start out very small and as the caterpillar grows and feeds, the bags enlarge until they are about an inch in length.
It’s at this time when most people begin to see them in the landscape (late summer).
Inspect plants now for the caterpillars. If you had bagworms last season, start with those plants and work your way around the landscape, paying close attention to the evergreens.
You are looking for a very tiny caterpillar that might already have some pieces of foliage attached.
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